Proportional motor control arrangement



Oct.`1, 1968 J. DIDWALL -PROPORTIONAL MOTOR CONTROL ARRANGEMENT Filed Sept. 1, 1965 2 Sheets-Sheet 1 mJOn. QmQdIw moho: u moon. omrm LII Oct. l, 1968 J. DIDWALL. 3,404,325

PROPORTIONAL MOTOR CONTROL ARRANOEMENT Filed Sept. l, 1965 2 Sheets-Sheet 2 y u i v'- NO SIGNAL -f -fL MMM l y DOWN SIGNAL u v v- UP SIGNAL Y NO SIGNAL INVENTOR.

JOSEPH D/DWALL Bm .m

AT RNEY United States Patent O1 ice 3,404,325 Patented Oct. 1, 1968 3,404,325 PROPORTIONAL MOTOR CONTROL ARRANGEMENT Joseph Didwall, Loreley Beach Road, White Marsh, Md. 21162 Filed Sept. 1, 1965, Ser. No. 484,237

, 1 Claim. (Cl. S18-208) ABS'I'RAC'II` 0F THE DISCLOSURE A motor control arrangement utilizing the instant switching action of silicon controlled rectitiers to close the appropriate shading coil circuit for a reversible induction motor. The .anodes of the rectifiers are powered through a direct connection to the shading coils where a voltage is reduced by transformer action from the motor running coil. f

This invention relates generally to electric motor control devices, and more particularly it pertains to a system for more accurately plugging positioning motors.

The operation of braking an electric motor by arranging the connections so it tends to run in the reverse direction is widely used for positioning mechanical devices. Often the circuiting is arranged with supplemental feedback from the motor so the system is responsive t-o an introduced error signal which may be very small. Thus, there is a magnification of any positioning inaccuracies and often jitter and erratic operation of oscillation nature occurs and is difficult to overcome.

An object of the present invention is to provide a proportional motor control Iarrangement which uses silicon control rectiliers in conjunction with induction motors of the shaded coil type wherein the control increments of forward and reverse as well as hold are measured in fractions of a power line frequency cycle.

Another object of the invention is to provide .an electrical circuit arrangement which uses the rectifying properties of a silicon controlled rectier (SCR) as an elect trical brake for a motor.

Still another object of the invention is to provide an improved circuit for positioning a motor in accordance with a small command signal.

Other objects and attendant advantages of this invention will' become more readily apparent and understood from the following detailed specification and accompanying drawings in which:

FIG. l is a block diagram of a typical motor control arrangement embodying features of this invention;

FIG. 2 is a schematic diagram of the motor control of FIG. l;

FIG. 3 is the right hand portion of FIG. 2 enlarged for explanatory purposes;

FIG. `4 is a series of oscillograms showing the silicon controlled rectifier (SCR) drive signal; and

FIG. 5 is .a series of oscillograms of the output signal to the motor control windings.

With reference now toY FIG. 3 of the drawings, a shaded pole motor is shown by 'reference numeral 10. This motor has an induction type' armature 12 and a field or running coil 14. Such a motor 10 will only start and run if a s'horted one turn or more copper shading winding is incorporated into the pole pieces of the running coil 14.

If two such shading windings are suitably placed on the pole pieces and their leads brought out, a short circuit on one coil will cause the motor 10 to start and run in a forward direction. Conversely, a short circuit on the other coil will cause reverse starting and running of the motor 10.

The forward shading winding 16 for purposes of this invention is brought to the anode .and cathode terminals of a silicon controlled rectifier or SCR 20. The reverse s'had- CII ing winding 18 is similarly connected to another SCR 22. The running coil 14 is connected to a source of AC power as shown. The anode-to-cathode voltage for each SCR 20' and 22 is solely that AC voltage induced from the running coil 14 into the respective shading windings 16 and 18 of the motor 10 and is insuthcient to breakdown the SCRS 20 and 22.

A pushpull transformer 24 is provided which has a center tapped output winding 26. One end of this winding 26 is connected to the gate terminal of SCR 20, the other end to the gate terminal of SCR 22. The cathodes of both SCRs 2.0 and 22 are connected together and also connect to the center tap of output winding 26.

When a symmetrical AC signal or an alternate positive and negative going pulse is introduced to the primary 28, it swings the ends of the center-tapped output winding 26 alternately positive and negative. When the resulting positive ga-te-to-cathode rigger current flows in an SCR 20 or SCR 22, it tires and conducts while a positive potential exists across anode-to-cat-hode.

This requirement is fulfilled by synchronizing the trigger impulse with the AC supplied to the running coil 14 of the motor 10. With reference to FIG. 2, a chopper 30, which may be of any of the well-known types, is driven by the same 110 volt AC supply as the running coil 14 of the motor 10. This chopper 30= connects to the input of an amplifier 32, which, in turn, connects `to the primary 28 of the -pushpull transformer 24. Thus, a DC signal E is presented to the input terminals 44 of the chopper 30 and it is modulated to a pulse form of the same polarity for the amplifier 32 to amplify, only one SCR will lire ,and short a shading winding, and the motor 10 will consequently rotate. A DC signal of opposite polarity will cause reverse opertion of the motor 10.

In the present example the resulting firing of one or the other SCRs 20 or 22 and movement of the armature 12, is fed back by a mechanical connection 36 to the arm 38 of a potentiometer 40 having a standard cell 42.

The voltage developed by this potenti-ometer 40 is connected in series opposition to the signal E and the combined voltages fed to the input terminals 44 of the chopper 30. The transformer 24 is poled so as to lire the SCR 20 or SCR 22 whichever results in a rotation of motor 10 which tends t-o equalize the voltages of the potentiometer 40 with the signal E. Consequently, the position of the armature 12 can be used to indicate the potential of the signal E by means of a linkage and pen 46 as shown in FIG. 1. Other uses will suggest themselves to those skilled in the art.

The superiority of the yabove described control is mani-- fested in the positive manner in which the motor 10 responds and stops without coasting. It is believed this is because there is a braking action on the armature of motor and displaced degrees between the shading windings 16 and 18. This is occurring at the power line frequency and so is very rapid in action.

FIGS. 4 and 5 depict the wave forms Iat the gate and an-ode respectively of the SCRs as used in the novel circuit.

Obviously, many modifications and variations of the present invention .are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A proportional motor control arrangement, compris-A ing, an AC motor having an induction type armature, a running coil, .and a forward shading coil and a reverse shading coil, an AC power source for said running coil, a first silicon controlled rectifier having an anode and a cathode connected directly to said forward shading coil, and a second silicon controlled rectifier having an anode ters, gating means for each rectifier, a push-:puik trans former having a center tapped output winding, said center tap connected to said comni'on cathode connection, each opposite vend -of said output winding being vconnected -to a respective gating means, lamplifier means coupled to said transformer, a control voltage of a frequency like-said AG source and off'reversible.polarityv connected to said amplifier, whereby -a selected polarity will gate only one 'of said rectiers and short circuiton'e of said shading coils causing said AC motor to run in one direction and a short circuiting on' the other of`said shadingcoils will cause said- AC motor to run in the reverse direction.

UNITED 1/1949 s/1950 2/1957 z/1960 4"//11962A A8/1965Y "1/,1966- -741966 STATES PATENTS 

